The use of modified tannin polymers has been known. One popular product is a reaction product of tannin/amine and formaldehyde that is used as a water clarification product. These types of products have demonstrated good performance, for example, in the removal of residual oil from wastewater. However, in certain instances, these reaction products must be made by complex and sensitive manufacturing processes and they may also pose storage and short product shelf life issues.
Byproducts such as secondary and tertiary amines are often formed during the preparation of these products, resulting in increased cost and an unstable product. Another problem is formation of gaseous carbon dioxide, which causes foaming and minimizes loading of reactors during manufacturing, thus increasing manufacturing costs.
The manufacture of these tannin/amine/formaldehyde reaction products also results in significant levels of formaldehyde on the order of 3,000-4,000 ppm and more. Formaldehyde can result in immune system problems and is also a cancer hazard. Exposure to formaldehyde can be irritating to the eyes, nose, and throat and can cause coughing and wheezing. Prolonged exposure can cause severe allergic reaction of the skin, eyes and respiratory tract.
Recently, residual formaldehyde levels have been subjected to increased global security and materials containing more than 1,000 ppm of residual formaldehyde are being banned or limited in commercial applications due to human and environmental hazards. Attempts at increasing the temperature or time of the tannin/amine/formaldehyde reaction to drive the residual formaldehyde to less than 1,000 ppm causes unwanted crosslinking of tannin, gelling and solidification of product batches.
Removal of formaldehyde from the known tannin/amine/formaldehyde products is challenging. Formaldehyde exists in the aqueous reaction product solutions in a polymeric or hydrated form. The latter is referred to as methanediol and has a boiling point of 194° C. Thus, it is impossible to distill this compound from aqueous solutions.
Formaldehyde scavengers may be used in order to reduce formaldehyde concentration levels. However, due to the low concentration of formaldehyde in the aqueous reaction media, multiple stoichiometric excesses of formaldehyde scavenger are necessary, resulting in increased costs, toxicity, and reduced activity of the desired amine/tannin product.